diff --git a/crates/calc/src/eval.rs b/crates/calc/src/eval.rs
index 92a0a39..65de8b0 100644
--- a/crates/calc/src/eval.rs
+++ b/crates/calc/src/eval.rs
@@ -1152,7 +1152,8 @@ impl<'h> Evaluator<'h> {
         }
         match src {
             Ev::R(areas) => {
-                let Some(a) = areas.get((area_n - 1).max(0) as usize).copied() else { return err(CellError::Ref) };
+                let area = usize::try_from((area_n as u64).saturating_sub(1)).ok();
+                let Some(a) = area.and_then(|i| areas.get(i)).copied() else { return err(CellError::Ref) };
                 let r = a.range;
                 // A single row or column with one index picks along it.
                 let (row, col) = if two_args && r.height() == 1 { (1, row) } else { (row, col) };
diff --git a/crates/calc/src/tests.rs b/crates/calc/src/tests.rs
index 5133409..aa9d460 100644
--- a/crates/calc/src/tests.rs
+++ b/crates/calc/src/tests.rs
@@ -157,6 +157,21 @@ fn index_with_arrays_of_positions() {
     assert_eq!(t.num("E7"), 6.0);
 }
 
+#[test]
+fn index_area_number_overflow() {
+    let mut t = T::new();
+    t.set("A1", "7");
+    t.set("D1", "9");
+    for (area, expected) in [("1", 7.0), ("2", 9.0)] {
+        t.set("G5", &format!("=INDEX((A1:B2,D1:E2),1,1,{area})"));
+        assert_eq!(t.num("G5"), expected, "area {area}");
+    }
+    for area in ["3", "1E300", "-1", "-1E300"] {
+        t.set("G5", &format!("=INDEX((A1:B2,D1:E2),1,1,{area})"));
+        assert_eq!(t.get("G5"), Value::Error(CellError::Ref), "area {area}");
+    }
+}
+
 #[test]
 fn errors_and_cycles() {
     let mut t = T::new();